Comments about Canon Canon WP-DC35 Waterproof Housing for PowerShot S90 Digital Camera:

I bought this housing for scuba diving. And I like it a lot. The S90 is a great camera. In this housing it makes for a very compact U/W set up. Actually, the camera handles better in the housing than without. That's because the S90 is so small. With the housing you have a much better grip.

You can use almost all controls. The only thing missing is the back control ring. That can be simulated by using the "shortcut" and "left/right" buttons. Not so handy, because you need two hands to do that.
I set the shortcut button to set the custom white balance. So as I change depth, I only need one button press to set my white balance. Perfect! On my previous A610 I needed "set", "down", "menu", "set" to do the same.
The front control ring is great to set exposure compensation. And it's on the left side, which is perfect. Ikelite's housing has the ring control on the right. One reason not to buy that one. Others are the price and the size. But Ikelite's housing goes to 200 feet and Canon's only to 130. Well,probably a bit deeper, but who knows? I have taken my Canon A610 housing to 150 feet without a problem. Controls were still fine and no leakage.
Please note that (all?) Canon housings float. So if you hang it on your BCD, it's sometimes hard to find back. ;-) I always have my camera in my hand, so it's no big deal. Canon sells overpriced weights, but a lead weight or some stainless steel with a bolt will do a better job of keeping your camera on the bottom.
Also, Canon housings don't have filter threads. So it's hard to add color filters or wide angle adapters.
I am very happy with this housing.